Biochemically enchanced thermophilic treatment process

ABSTRACT

The present invention provides a process and apparatus for autothermal aerobic thermophilic treatment of high strength and high temperature wastes. In accordance with the process of the present invention, waste material is injected into a reactor vessel having thermophilic microorganisms to form a volume of bulk liquid in the reactor vessel. An oxygen-containing gas is also injected into the reactor vessel in such manner as to transfer oxygen into the reactor bulk liquid for utilization by the thermophilic microorganisms in aerobic treatment of the waste material. The oxidation-reduction potential and temperature of the reactor bulk liquid are monitored and at least a selected one of the rate of injection of the oxygen-containing gas, the oxygen-transfer efficiency of the oxygen-containing gas and the volume of bulk liquid in the reactor are adjusted in response to the oxidation-reduction potential and temperature of the reactor bulk liquid to maintain the temperature of the reactor bulk liquid within a predetermined range. This allows the system to match the oxygen transfer to the oxygen demand for the system. In particularly preferred embodiments, other parameters such as pH, COD, TS, VS, VFAs, NH 3  --N, PO 4  --P, alkalinity and sulfides in the reactor bulk liquid, as well as O 2 , CO 2 , and H 2  S in the offgas are monitored to provide further process information for optimization of the aerobic, thermophilic treatment process. Biological kinetic relationships developed by the inventor, and specific formulations of biological growth micronutrients are utilized for further enhancing the aerobic thermophilic treatment process.

RELATED APPLICATIONS

This application claims the benefit of Provisional Application No.60/071,943 entitled Biochemically Enhanced Thermophilic TreatmentProcess, filed Jan. 20, 1998.

FIELD OF THE INVENTION

The present invention relates generally to biological processing ofwaste material and, more particularly, but not by way of limitation, toan aerobic thermophilic treatment process for treating high temperatureor high strength wastes in various forms.

BACKGROUND OF THE INVENTION

Numerous processes have been developed over the years for biologicaltreatment of domestic and industrial wastewater and sludge. Thesebiological treatment processes include both aerobic and anaerobictreatment processes which use biologically active microorganisms (or"biomass") to convert various soluble contaminants, especially organiccontaminants, into a form which can be separated from the wastewater.Insoluble organic contaminants are digested by such processes to producea reduced quantity of a known biomass.

Although such biological treatment processes yield purified water, theyalso yield a net positive production of biological solids whichcontribute to the biomass used for the process. Consequently, a portionof the biomass (or sludge) must be periodically removed for furthertreatment or disposal. There are significant costs associated withfurther treatment of the biomass produced, and there are numerousregulations and significant costs associated with disposal of thebiomass. Thus, in recent years, much attention has been focused onminimizing the amount of biomass produced during the biologicaltreatment process.

In the mesophilic temperature range, about 50° F. to 110° F., the newbacteria generated as a result of the anaerobic treatment process isonly approximately 10 to 20 percent of that produced as a result of theaerobic treatment process. Furthermore, because methane from the biogasproduced during anaerobic treatment can be burned to provide heat to thesystem, the energy requirement for the anaerobic process is only about10 to 20 percent of that for the aerobic process at the sametemperature. A substantial drawback to the anaerobic treatment process,however, is that it produces a biogas which consists primarily ofmethane (CH₄), carbon dioxide (CO₂) and hydrogen sulfide (H₂ S). The H₂S in the biogas can cause severe odor problems and biological toxicity.Hydrogen Sulfide is an extremely corrosive gas and can be lethal in highconcentrations. With the increasingly stringent federal regulationsgoverning this area, the anaerobic treatment process is becoming lessand less desirable for many waste treatment applications.

As an alternative, aerobic treatment processes in the thermophilictemperature range, about 115° F. to 170° F., produce only about 10 to 20percent of the biomass generated from the aerobic process in themesophilic range. Additionally, the offgas produced from aerobictreatment primarily comprises carbon dioxide (CO₂), with essentially nohydrogen sulfide (H₂ S) production. Thus, aerobic thermophilic processesyield reduced biomass production comparable to mesophilic anaerobicprocesses, but without the associated noxious and odorous biogas.

Both soluble wastewater constituents and particulate or suspended solidmatter, such as waste biological sludges, can be used as a food or fuelsource for the thermophilic microorganisms. Solid matter first has to bebiochemically hydrolyzed to soluble constituents and transported acrossthe thermophilic microorganism cell wall before it can be used as a foodor fuel source by the microorganisms. The food or fuel value of thewaste material is best measured as chemical oxygen demand (COD) orvolatile solids (VS).

The COD can be measured or calculated. The calculated or theoretical CODrepresents the stoichiometric amount of oxygen which would be requiredto chemically oxidize all of the food, fuel, or organic matter in thewaste material to carbon dioxide and water. The COD value can becalculated when the composite empirical formula for the waste materialsbeing oxidized is known along with their relative concentrations.Otherwise, the COD can be measured by a standard COD test methodologyused to oxidize all the organic matter to carbon dioxide and water,whereby the associated oxygen equivalents are measured. Likewise, thevolatile solids content of a waste can be measured by a standard solidstest methodology, whereby the solids are burned in a furnace forgravimetric determination of the amount of solids volatilized or lost.Either the COD, VS, or both can be effectively utilized to measure theamount of substrate, food source, fuel, or organic matter available inthe waste for utilization by the thermophilic bacteria for growth,energy production, heat production, and cell maintenance.

As noted, the aerobic thermophilic treatment process generates heat andis, therefore, an exothermic process. Thus, if the waste to be treatedis sufficiently concentrated with organic compounds to serve as food forthe thermophilic bacteria in the reaction processes, the reactionprocess will be autothermal, i.e., the reaction will supply enough heatto maintain the temperature at the desired level within the thermophilicrange. Even if the waste is not a "high strength" waste, the reactioncan also be autothermal if the temperature of the waste is sufficientlyhigh.

Although high strength and high temperature wastes can, in theory, yieldan autothermal thermophilic process, in practice the prior art methodshave been unable to achieve this result in a commercially practicableprocess. The primary problem arises from the air that is injected intothe reactor to provide the oxygen necessary to react with thethermophilic bacteria. The air utilized for such processes is normallycompressed air which has been obtained from the ambient air surroundingthe treatment facility. This air is normally not 100% humidified and mayhave a temperature which is relatively low compared to the desiredthermophilic temperature of the sludge. Consequently, as the air risesthrough the liquid in the reaction vessel it will be humidified andheated. As the air exits the reaction vessel, heat is lost from thesystem and the temperature of the system is lowered. Thus, prior artmethods have required addition of heat to the process from an externalsource, increasing significantly the cost associated with the treatmentprocess.

Heightening the problem is the fact that in prior art processes only aportion of the oxygen available from the injected air will actually betransferred to the thermophilic microorganisms to supply the oxygendemand required for aerobic treatment. Thus, as more air must be passedthrough the reaction liquid to meet the oxygen demand because of pooroxygen transfer, more heat is lost in the offgas, and the temperature ofthe system will not support autothermal conditions. By contrast, if toolittle air is passed through the system, there will not be enough oxygentransferred to the thermophilic microorganisms for aerobic treatment ofthe waste, and the process will turn anaerobic with all of theassociated disadvantages.

Thus, there continues to be a need for a process for aerobicthermophilic treatment of wastewater and sludge. The process should beautothermal and should match the oxygen transfer to the oxygen demand.

SUMMARY OF THE INVENTION

The present invention provides an improved process and apparatus foraerobic thermophilic biological treatment of wastes in various forms.The improved aerobic thermophilic process utilizes specific parametermonitoring to optimize and control the treatment process.

In accordance with one embodiment of the invention, a process isprovided for the aerobic thermophilic treatment of waste, includinginjecting waste material into a reactor vessel having thermophilicmicroorganisms to form a volume of bulk liquid in the reactor vessel,injecting an oxygen-containing gas into the reactor vessel in suchmanner as to transfer oxygen into the reactor bulk liquid forutilization by the thermophilic microorganisms in aerobic treatment ofthe waste material, monitoring the oxidation-reduction potential andtemperature of the reactor bulk liquid; and adjusting at least aselected one of the rate of injection of the oxygen-containing gas, theoxygen-transfer efficiency of the oxygen-containing gas and the volumeof bulk liquid in the reactor in response to the oxidation-reductionpotential and temperature of the reactor bulk liquid to maintain thetemperature of the reactor bulk liquid within a predetermined range. Inparticularly preferred embodiments, other parameters such as pH, COD,TS, VS, VFAs, NH₃ --N, PO₄ --P, alkalinity and sulfides in the reactorbulk liquid, as well as O₂, CO₂, and H₂ S in the offgas are monitored toprovide further process information for optimization of the aerobic,thermophilic treatment process. Biological kinetic relationshipsdeveloped by the inventor, and specific formulations of biologicalgrowth micronutrients are utilized for further enhancing the aerobicthermophilic treatment process.

Similarly, the apparatus of the present invention includes means forinjecting an influent mixture into a reactor vessel having thermophilicmicroorganisms to form a volume of bulk liquid in the reactor vessel,wherein the influent mixture comprises an oxygen-containing gas, wastematerial and recycled effluent, means for monitoring theoxidation-reduction potential and temperature of the reactor bulkliquid, and means for adjusting at least a selected one of the rate ofinjection of the oxygen-containing gas, the rate of injection of therecycled effluent and the volume of the bulk liquid in response to theoxidation-reduction potential and temperature of the reactor bulk liquidto maintain the temperature of the reactor bulk liquid within apredetermined range.

These and various other features as well as advantages whichcharacterize the present invention will be apparent from a reading ofthe following detailed description and a review of the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the preferred embodiment of the reactorvessel of the present invention useful for practicing the biochemicallyenhanced thermophilic treatment process of the present invention.

FIG. 2 is a horizontal cross-sectional view taken at the bottom of thereactor vessel containing one possible arrangement for the influentdistributor piping associated therewith.

DETAILED DESCRIPTION

The present invention provides an improved process and apparatus foraerobic thermophilic biological treatment of high temperature or highstrength wastes in various forms (e.g., soluble, slurry,particulate/solid or combination forms). The improved aerobicthermophilic process utilizes specific parameter monitoring to optimizeand control the treatment process. Preferably, parameters are monitoredin both the reactor bulk liquid and the offgas or biogas produced.Biological kinetic relationships developed by the inventor, and specificformulations of biological growth micronutrients are utilized forfurther enhancing the aerobic thermophilic treatment process.

Illustrated in FIG. 1 is an aerobic thermophilic reactor for treatinghigh temperature or high strength wastes according to the process of thepresent invention. The aerobic thermophilic reactor of the presentinvention is generally designated by the reference numeral 10 andincludes reactor vessel 12 having a bottom floor 30 and a roof 54. Aninfluent waste source 14 designates the waste material to be treated bythe process, which may be any soluble, slurry, or solid waste, orvarious combinations thereof, having organic and/or other contaminantsparticularly suitable for thermophilic treatment as further describedherein. The waste material is pumped to the aerobic thermophilic reactor10 by an influent waste pumping system 16 through conduits 20, 22, and24 for ultimate mixing with the reactor contents (or "bulk liquid") ofreactor vessel 12. To regulate the flow of waste material to the reactorvessel 12, a flow meter 15 and control valve 17 are provided in conduit20. Alternatively, the flow of influent waste material can be regulatedby using a variable speed pump (not shown) for the waste pumping system16. A liquid level sensor 178 monitors the level of the bulk liquid inthe reactor vessel 12.

Increased flow is provided to conduits 20, 22, and 24 for mixingpurposes by recycling a stream of reactor effluent through recycle line18 to conduits 20, 22, and 24. Oxygen is provided for the aerobicprocess from an air source 25 or such other oxygen containing gassource. The flow of air (or other oxygen containing gas) is generated bya blower 152 and regulated by a flow meter 184 and a flow control valve186. Alternatively, the flow of air can be regulated by using a variablespeed blower (not shown) to generate the flow of air. The air travelsthrough conduit 140 to conduit 20 where it is added to the influentwaste material and recycled effluent in conduit 20 to form an influentmixture in conduits 22, 24 as it is conveyed to the reactor vessel 12for mixing with the reactor bulk liquid.

Referring now to FIGS. 1 and 2, the influent mixture in conduits 22, 24is distributed by a system of influent distributor pipes 26, 28 alongthe reactor floor so as to evenly distribute the flow of influentmixture across the entire area of the reactor vessel 12. The influentdistributor pipes 26, 28 contain orifices or nozzles 29 at intervalsalong their length which results in the influent mixture exiting thedistributor pipes 26, 28 at high velocity, thereby imparting high oxygentransfer efficiency and mixing energy to the reactor bulk liquid toprevent settling of the biological solids within the reactor vessel 12.The influent distributor pipes 26, 28 are valved (not shown) to allowisolation of areas of the distributor pipes 26, 28 to force all of theinfluent mixture flow through a portion of the distributor pipes 26, 28to help prevent the accumulation of deposits in the distributor pipes26, 28 and orifices or nozzles 29 and to agitate the reactor vessel 12to prevent packing of sludge on the bottom floor 30 of the reactorvessel 12. Further details of construction as to this and perhaps otheraspects of the present invention can be determined from a reading of theinventor's prior patent, U.S. Pat. No. 5,228,995, which is incorporatedherein by reference.

Upon entering the reactor vessel 12, the influent mixture assumes avertical flow path 32 and mixes with thermophilic biological solids in asuspended growth zone 34. The upward flow path 32 of the air, influentwaste and recycled effluent of the influent mixture serves to maintainthe biological solids in suspension in the suspended growth zone 34.

Offgas is withdrawn from the reactor vessel 12 through the headspacearea 56 above the liquid line 52 and below the roof 54 of the reactorvessel 12 under negative pressure supplied by offgas blower 104. Thereactor vessel 12 is air-tight to prevent unwanted air from entering thereactor vessel 12 and to allow the offgas blower 104 to create anegative pressure in the headspace area 56.

The aerobic thermophilic reactor 10 can be operated in a constant volumeor variable volume mode. In the constant volume (or liquid level) mode,treated effluent is withdrawn from the reactor vessel 12 though an uppereffluent withdrawal line 50 by gravity or an upper effluent pump 53.When using upper effluent pump 53, the amount of treated effluentleaving the aerobic thermophilic reactor 10 through conduit 72 isregulated by an effluent flow meter 58 and an effluent flow controlvalve 60. As noted above, a portion of the treated effluent is splitfrom the upper effluent withdrawal line 50 via line 74 for recyclingthrough recycle line 18 and the influent conduits 20, 22, 24 to thereactor vessel 12. Flow for the recycle stream is provided by a recyclepump 76 and a recycle flow meter 180 and recycle flow control valve 80to regulate the flow rate for the recycle stream through recycle line18. The flow rate for the recycle stream is designed to provide theoptimum hydraulic throughput rate to maintain adequate and effectivemixing intensity, efficient oxygen transfer, and suspension of thebiological solids in the suspended growth zone 34. The recycle pump 76typically includes two or more pumps (not separately designated) toallow flexibility in operation.

In the variable volume (or variable liquid level) mode, the recycleeffluent and treated effluent are removed from the reactor vessel 12through a lower effluent withdrawal line 134 by lower effluent pump 136and the treated effluent is discharged through line 138. The flow ratefor the treated effluent discharged through line 138 is regulated byeffluent flow meter 200 and effluent control valve 202. A portion of thetreated effluent is split from line 134 to line 135 and pumped byrecycle pump 76 for recycle through line 18, as described above.

It is characteristic of thermophilic treatment reactors which operate athigh temperatures that as the offgas rises to the top of the reactorvessel 12 into headspace area 56, some solids are also carried to thesurface of the liquid line 52 contributing to form a foam/scum layerwhich provides a layer of insulation for the aerobic treatment process.Control of this characteristic foam/scum layer is necessary to ensureoptimal performance of the aerobic thermophilic reactor 10. To controlthe foam/scum layer, the aerobic thermophilic reactor 10 is equippedwith a foam/scum overflow line 81 which serves to set the maximum heightof the foam/scum layer. The foam/scum is conveyed to either a foam/scumcollection chamber or may be combined with the treated effluent.

Preferably, the aerobic thermophilic reactor 10, is also provided with afoam spray control system 82 which utilizes a portion of the internalrecycle flow on conduit 83 for antifoam spray water. The spray water isapplied as a coarse spray water onto the foam/scum surface to break upthe foam/scum by a number of spray nozzles 84 located near the roof 54of the reactor vessel 12. Control of the spray water through conduit 83is provided by control valve 85.

Offgas generated by the aerobic thermophilic treatment process iswithdrawn from the reactor vessel 12 by the offgas blower 104 via theoffgas removal line 92. The offgas blower 104 is used to convey theoffgas to an appropriate treatment or scrubbing system or to arecycle/reuse application in a liquid processing wastewater treatmentplant for reuse of the ammonia-nitrogen nutrient generated from sludgeprocessing.

In accordance with the present invention, optimization of the aerobicthermophilic treatment process is achieved by monitoring and controllingthe temperature, pH and ORP of the reactor bulk liquid to maintain thesecritical parameters within appropriate ranges. Thus, a temperaturesensor 166, a pH sensor 168 and an ORP sensor 170 are provided tomonitor these critical parameters of the bulk liquid.

A pH range of 6.5 to 9.0 is needed for effective operation of theaerobic thermophilic reactor 10. Since most high strength wastes areacidic, and alkalinity is consumed during treatment, it is normallynecessary to supplement the wastewater with alkalinity in order tomaintain a proper operating pH range in the reactor vessel 12. Anexception is waste biological sludge which produces excess alkalinity inthe form of ammonium bicarbonate alkalinity during thermophilicdigestion or treatment. No pH adjustment is made to the influent wastebefore mixing with the recycle stream in order to make beneficial use ofthe alkalinity and buffering capacity of the recycle stream. Sodiumhydroxide NaOH or calcium hydroxide Ca(OH)₂ are added from a causticsource 142 using a variable speed pump 154 as needed for alkalinityaddition for final pH control. The pH sensor 168 is thus provided tomonitor the pH inside the reactor vessel 12 so that the pH can bemaintained within the predetermined set point range.

As noted above, in the process of the present invention it is importantto match the oxygen transfer to the oxygen demand. However, because bulkliquid dissolved oxygen (D. O.) levels are so low (0.1 to 0.5 mg/l) andthe dissolved oxygen uptake rates (DOURs) are so high (normally 200 to500 mg/l/hr.) in aerobic thermophilic systems, it is impossible toaccurately measure the D.O. level in the reactor vessel 12. Thus, thepresent invention uses ORP as an indicator of the D. O. level of thereactor bulk liquid and the ORP sensor 170 is the means for monitoringthis parameter. The desired ORP for any given system will vary dependingupon factors such as the characteristics of the waste material to betreated, the reactor design, etc. However, in many reactors thepreferred operating range for the ORP will be from about -300 mV toabout 0 mV.

Temperature is another critical parameter in the process of the presentinvention. It is important that the temperature of the reactor bulkliquid remain within the thermophilic temperature range (115° to 170°F.) and preferably within the optimum temperature range of 135° to 145°F. for the process to remain autothermal or self-heating. Temperaturesensor 166 allows monitoring of the temperature of the reactor bulkliquid so that this parameter can also be maintained within the setpoint range, preferably at the upper end of the preferred thermophilictemperature range.

As shown in FIG. 1, a supplemental heating system 128, consisting of asteam source 132 and injector valve or heat exchanger 130, can also beprovided to heat the influent flow or recycle line 18 in the event theheating requirements of the aerobic thermophilic reactor 10 cannot besatisfied by the fuel value content or the temperature of the raw wasteto be treated. Such a supplemental heating system allows the reactorbulk liquid temperature to be maintained within the desired temperaturerange.

The temperature sensor 166 and ORP sensor 170 are provided to monitorthese primary parameters of the bulk liquid in order to effectivelymatch the oxygen transfer to the oxygen demand. If the temperature orORP are outside the respective set point ranges, the system is optimizedby adjusting the flow rates of the recycle effluent and air using flowcontrol valves 80, 186.

In highly preferred embodiments, secondary parameters are also monitoredto give further information as to the state of the reaction processtaking place in the reactor vessel 12. An oxygen sensor 172, a carbondioxide sensor 174 and a hydrogen sulfide sensor 176 are provided in theoffgas removal line 92 for monitoring the levels of each of these gases.While preferred ranges for each of these parameters may vary, in manywaste treatment applications oxygen in the offgas will preferably be inthe range of 10 to 15 percent and hydrogen sulfide will preferably beless than 10 parts per million. The carbon dioxide concentration in theoffgas will be plant specific. Furthermore, volatile fatty acid (VFAs)and sulfide concentrations in the reactor bulk liquid are monitoredusing wet chemistry analysis of samples taken from the reactor bulkliquid. In many waste treatment plants, the preferred range for VFAswill be less than about 1500 mg/L and the preferred range for sulfideswill be less than about 1.0 mg/L. Each of these parameters providesfurther information as to the state of the aerobic treatment process andthe adjustments needed to the flow rates of the recycle effluent and airin order to maintain the process as both aerobic and thermophilic.

The oxygen sensor 172 determines the concentration of oxygen in theoffgas and gives an indication of the oxygen which is passing throughthe system without being utilized for the reaction processes takingplace in the bulk liquid. The carbon dioxide sensor 174 determines thelevel of carbon dioxide in the offgas and can be used to determine theamount of carbon dioxide generated as offgas.

Table one summarizes, typical preferred ranges for the primary andsecondary process parameter.

                  TABLE 1                                                         ______________________________________                                        Parameter             Preferred Range                                         ______________________________________                                        Temperature, T        135° F. to 145° F.                        Oxidation Reduction Potential, ORP                                                                  -300 mV to 0 mV                                         pH                    6.5 to 9.0                                              Volatile Fatty Acids, VFAs                                                                          <1,500 mg/L                                             Sulfides              <1.0 mg/L                                               Oxygen, O.sub.2 (in the offgas)                                                                     about 10 to 15%                                         Hydrogen Sulfide, H.sub.2 S (in the offgas)                                                         <10 ppm                                                 Carbon Dioxide, CO.sub.2 (in the offgas)                                                            Plant Specific                                          ______________________________________                                    

If the ORP is allowed to reduce enough to allow anaerobic bacteria tothrive, sulfides can be produced from wastes containing sulfates and/ororganic sulfur containing compounds. This will yield sulfides in thebulk liquid. Hydrogen sulfide (H₂ S) is partially soluble and insoluble,and as the H₂ S is produced above its solubility level, it diffuses outof solution and into the offgas. This is a normal aspect of anaerobicsystems and the amount of sulfides in the bulk liquid and H₂ S in thebiogas must be monitored and controlled to achieve maximum treatmentperformance. The sulfides level in the reactor bulk liquid is determinedusing wet chemistry techniques, while the H₂ S level in the offgas isdetermined using the H₂ S sensor 176.

At the very low D. O. and ORP levels associated with the aerobicthermophilic process of the present invention, fermentation reactionswill exist with some VFA formation. As the D. O. and ORP levels decline,VFAs produced from fermentation reactions will increase. VFA formation,if allowed to accumulate to high levels in the reactor, can causebiological feedback inhibition and reduced treatment performance. Inaccordance with the present process, VFAs are conveniently monitoredusing wet chemistry techniques.

Thus, monitoring oxygen, carbon dioxide and hydrogen sulfide in theoffgas, as well as VFAs and sulfides in the reactor bulk liquid inaccordance with the process of the present invention provides furtherinformation as to the conditions in the reactor vessel 12. Suchinformation, in combination with the bulk liquid ORP, is used to insurean appropriate oxidizing environment in the aerobic thermophilic reactor10.

Besides the chemical feed system for the caustic source 142, four otherchemical feed systems are provided to provide sources of other chemicalsnecessary to optimize the treatment process. Variable speed pumps 154,156, 158, 160, 162 control the rates of the respective sources 142, 144,146, 148, 150 which are supplied to the recycle line 18. A lime source144 provides alkalinity and calcium as a micronutrient. A ferrouschloride (FeCl₃) and/or ferric chloride (FeCl₂) source is provided toprovide these chemicals as micronutrients, for odor control, and forsulfide complexation, if needed. Either FeCl₃ or FeCl₂ can be used forsulfide control by complexing or precipitating sulfides as they areformed in the reactor. However, sulfate reduction to sulfides isprimarily controlled by controlling the ORP, and thus the oxygen, in thereactor vessel 12.

A macronutrients (nitrogen and phosphorus) source 148 and amicronutrients (trace metals) source 150 are provided because suchnutrients are critical to successful performance of thermophilictreatment systems, especially when treating nutrient deficient wastes.The levels of the macronutrients nitrogen and phosphorus are normallyinadequate in high strength industrial wastes. Aqueous ammonia andphosphoric acid can be used to supply nitrogen and phosphorus, as wellas various forms of fertilizers. The micronutrient source 150 providesthe following primary chemicals necessary for growth requirements:

Ferric chloride/ferrous chloride;

Calcium chloride;

Ammonium molybdate;

Nickel chloride;

Copper sulfate;

Cobalt chloride; and

Zinc sulfate.

The trace metals are critical in controlling the rate of enzymereactions which set the rate of biological activity. Trace metals alsoserve as regulators of osmotic pressure and to transfer electrons inoxidation-reduction reactions such as the storage of energy, i.e., theconversion of ADP to ATP. The major trace elements required by bacteriainclude iron, magnesium, calcium, copper, zinc, nickel, cobalt,molybdenum, selenium and tungsten. Any of these micronutrients can beadded to the reactor vessel 12 in low concentrations, as necessary tostimulate the thermophilic bacteria.

In highly preferred embodiments, the various monitor and controlelements of the aerobic thermophilic reactor 10 are regulatedautomatically by means of a PLC 164, which includes a computer linked tothe various monitoring and control elements, as shown in FIG. 1.

As noted above, the most effective indicators of thermophilic reactorperformance are bulk liquid temperature, pH, ORP, VFA's, and sulfides,along with offgas or biogas oxygen, carbon dioxide, methane, and H₂ Scontent. Additionally, though, alkalinity, COD, TS, VS, NH₃ --N, PO4--Pand micronutrients can be monitored in the bulk liquid to provide stillfurther process information. Each of these parameters should be keptwithin desired operating ranges which are plant specific in nature. Anunderstanding of the interrelationships and interdependence of all theseparameters, along with proper monitoring and control is required forsuccessful start-up and operation of aerobic thermophilic reactor 10.From the following discussion, the significance of each of theseparameters will be apparent to those skilled in the art.

One aspect of thermophilic treatment of waste biological sludges is therelease of organically bound nitrogen as NH₃ --N. Actual nitrogenmeasurement in waste biological sludges indicate nitrogen contents frombetween about 7.0 to 12.0% by weight. Therefore proteinaceous wastes,like biological sludges, generate excess nitrogen in the ammonia formwhich reacts with the excess CO₂ in the reactor bulk liquid to reducethe amount of free bulk liquid CO₂ and headspace CO₂ partial pressure byproducing ammonium bicarbonate alkalinity (NH₄ HCO₃). A significantportion of the CO₂ that is produced from the biological activity doesnot replace oxygen in the gas phase, but instead the CO₂ reacts with theammonia and remains in the aqueous phase (bulk liquid). For each mg/l ofNH₃ -N formed, 5.6 mg/l of NH₄ HCO₃ alkalinity is formed, which isequivalent to 3.6 mg/l of calcium carbonate (CaCO₃) alkalinity. Theammonium bicarbonate alkalinity causes the reactor bulk liquid pH toincrease; with highly proteinaceous wastes the pH typically increases tothe 8.0 to 9.0 pH range. At these high bulk liquid pH levels and thehigh temperatures associated with the thermophilic process a portion ofthe NH₃ --N formed will be volatilized or released into the reactoroffgases. When the thermophilic system offgases are treated byabsorption back into biological liquid treatment systems (for exampleactivated sludge systems) the NH₃ --N released in the offgases iscaptured for recycle/reuse for new biological growth. Highconcentrations of NH₃ --N, PO₄ --P, and micronutrients released into thethermophilic reactor bulk liquid when treating waste biological sludgescan also be recycled and reused back in the wastewater biologicaltreatment process for synthesis of new biological cells (waste sludge).When the thermophilic waste sludge is dewatered, the filtrate isrecycled back to the mesophilic biological treatment process.

Proper sizing and evaluation of aeration equipment for the transfer ofthe required amount of oxygen into the aerobic thermophilic reactorrequires determination of the oxygen utilization (uptake) requirementsand an understanding of the interfacial resistances to oxygen transferand the oxygen solution characteristics of the waste matrix to betreated. Increasing or decreasing the air or oxygen flow rate into thereactor affects the oxygen transfer rate, type of and rate ofbiochemical reactions, heat loss and temperature, and nature of anddegree of foaming. It is, therefore, very critical to match the air oroxygen flow rate and oxygen transfer efficiency with the oxygenutilization rate in the aerobic thermophilic reactor design andoperations. Since it is practically impossible to measure the DOUR's atsuch high rates and low bulk liquid D. O.'s, an alternative approachmust be used to estimate the required oxygen utilization rates.

In accordance with the present invention, a more readily facilitatedmethod for determining the oxygen utilization requirements for anyspecific waste is to perform a stoichiometric energy balance, in whichall components of the balance are expressed in terms of oxygen, i.e., asCOD and oxygen uptake. If a certain amount of oxygen is required tocompletely oxidize the organic matter in the waste (soluble orparticulate), and only part of it is oxidized, then the remaining CODshould be equal to the original COD minus the oxygen equivalent that hasbeen expressed as oxygen uptake, as shown:

    COD.sub.W +COD.sub.S →O.sub.2 uptake+COD.sub.E +COD.sub.FS 1)

where:

COD_(W) =Waste COD

COD_(IS) =Initial Biological Solids COD

COD_(E) =Effluent COD

COD_(FS) =Final Biological Solids COD

Since COD_(W) -COD_(E) represents the delta change in COD due totreatment (ΔCOD), and COD_(FS) -COD_(IS) represents the increase inbiological solids expressed as COD, or ΔCOD (biological solids),Equation 1 can be written, as shown:

    ΔCOD=O.sub.2 uptake+ΔCOD (biological solids)   (b 2)

This balance represents the partition of the substrate betweenrespiration and synthesis. The amount of COD which has been oxidized isrepresented by the accumulated oxygen uptake.

Rearranging Equation 2 and realizing that ΔCOD (biological solids)equates to the COD of the waste biological sludge produced, thefollowing simplified equation can be utilized, as shown:

    O.sub.2 uptake=ΔCOD-COD (waste sludge)               (3)

Equation 3 should be used for thermophilic activated sludge type systemswith solids/liquid separation and return sludge and waste sludge typicalof conventional activated sludge systems. However, in once-throughthermophilic systems, such as those treating low flow, highconcentration wastes like slurries or particulate solids, all the wastesludge exits the reactor in the treated effluent. This operationalapproach simplifies the COD material balance to influent total COD minuseffluent total COD equals the oxygen utilized, as shown:

    O.sub.2 uptake=Influent COD-Effluent COD                   (4)

or

    O.sub.2 uptake=ΔCOD                                  (5)

This very simple energy balance approach using oxygen equivalentsprovides an easy and reliable methodology for estimating oxygenutilization requirements in thermophilic aerobic treatment systems.

The COD material balance methodology provides the ideal approach forestimating oxygen uptake requirements in thermophilic aerobic treatmentsystems. The increase in biological solids or waste biological solidsfrom industrial or municipal biological wastewater treatment systems canbe expressed in terms of oxygen equivalents (COD), either by directmeasurement or calculation. One of the major applications of the presentprocess is anticipated to be digestion treatment or stabilization ofthese wastewater treatment plant waste biological solids. Thesebiological solids are typically measured as total solids (TS) along withdetermination of the volatile fraction or volatile solids (VS). Using anempirical formula for the waste sludge or biological cells as measuredby VS, the oxygen required to oxidize the VS completely to CO₂ and H₂ Ocan be calculated, thus providing the theoretical COD of the biologicalsludge. The empirical formula employed below in the balanced equationfor total oxidation can therefore be used to calculate oxygenrequirements, as shown:

    C.sub.5 H.sub.7 NO.sub.2 +5O.sub.2 →5CO.sub.2 +2H.sub.2 O+NH.sub.3 ( 6)

The ratio of combining the weights for the biological cells and oxygenis equal to 1.42; thus each milligram of biological solids is equivalentto 1.42 milligrams of oxygen, or the calculated COD of the biologicalcells equals 1.42 times the dry weight of the cells measured as volatilesolids. Therefore, oxygen equivalents or oxygen utilization rates can bedetermined by either COD and/or VS measurements.

High field oxygen transfer efficiencies have been observed in theprocess of the present invention. In addition to exhibiting excellentoxygen transfer performance, the aerobic thermophilic process possessother desirable characteristics, such as; high operating temperatures,high oxygen utilization rates, tendency to foam, and high totaldissolved solids (TDS) concentrations. In air operated systems,evaporation losses account for a significant reduction in the bulkliquid volume treated along with associated increases in the inorganicTDS concentrations. The reduction in surface tension, in conjunctionwith high TDS concentrations, along with the previously discussedfactors impacting oxygen transfer in thermophilic systems all havepositive beneficial impacts on field oxygen transfer performance in theaerobic thermophilic treatment process at high temperatures.

Oxygen transfer in wastewater treatment involves the absorption of gas(oxygen) by a liquid whereby the physical mass transport across atwo-film layer consists of a gas film and a liquid film. The oxygentransfer rate can be expressed by the following equation:

    N=K.sub.L A(C.sub.S -C.sub.1)                              (7)

where:

N=Mass of oxygen transferred per unit time.

K_(L) =Liquid film mass transfer coefficient.

A=Interfacial area per unit volume.

C_(S) =Saturation concentration of oxygen at the gas/liquid interface.

C₁ =Concentration of oxygen in the bulk liquid.

The value K_(LA) is considered as the overall mass transfer coefficientand includes the liquid film coefficient and the interfacial area perunit volume. The "combined" coefficient is used because it isimpractical to measure the liquid film coefficient or the interfacialarea. The overall oxygen transfer process has been hypothesized to occurin three phases, as follows:

A. Transfer of oxygen molecules to the liquid surface resulting in anequilibrium or saturation condition at the gas/liquid interface.

B. The passing of oxygen molecules through the liquid film into solutionby molecular diffusion.

C. Mixing of oxygen in the bulk liquid by diffusion and convection.

Aeration equipment is typically rated by the oxygen transfer efficiencyin clean water (SOTR), assuming 0.0 mg/l dissolved oxygen, 1.0atmosphere pressure, and a temperature of 20° C. To translate fromstandard conditions to field process conditions the following equationis used: ##EQU1## where: AOR=Actual (Process) Oxygen Requirement(lb/hr).

SOR=Standard Oxygen Requirement (lb/hr).

α(Alpha)=Ratio of oxygen transfer coefficient (K_(LA)) of the wastewaterto that of tap water.

β(Beta)=Ratio of oxygen saturation of the wastewater to that of tapwater.

C_(wait) =Surface saturation dissolved oxygen concentration in cleanwater at the wastewater temperature (T_(w)) and basin elevation, mg/l.

D_(C) =Depth Correction Factor, Dc=Water Depth (ft)/100+1.

C_(L) =Residual Dissolved Oxygen concentration, mg/l.

C₂₀ =Surface saturation dissolved oxygen concentration of air in cleanwater at 20° C. and 760 mm Hg (9.09 mg/l).

θ(Theta)=Temperature correction coefficient.

T_(W) =Wastewater temperature (°C).

Wastewater contaminants, temperature, dissolved oxygen concentration,type of aeration device, and turbulence all affect oxygen transfer rate.The three parameters that account for the impact of these influences onoxygen transfer are alpha (α), beta (β), and theta (θ).

Alpha (α), the ratio of process water to clean water volumetric masstransfer coefficient, is different for different types of aerationdevices. The impact of wastewater contaminants can be attributed todissolved salts (inorganic TDS) and surface active agents. Thecalculation of alpha is represented by the following equation: ##EQU2##where: α=Alpha.

K_(LA) wastewater=Overall mass transfer coefficient of wastewater.

K_(LA) clean water=Overall mass transfer coefficient of clean water.

Beta (β) is defined as the ratio of the saturation dissolved oxygenconcentration of actual wastewater to that in clean water. Temperature,barometric pressure, and dissolved solids are the key variables thataffect the appropriate beta value. The aeration device is not consideredto have an impact on the beta factor. The calculation of beta isrepresented by the following equation: ##EQU3## where: β=Beta.

C_(wastewater) =Saturation concentration of oxygen in wastewater, mg/I.

C_(clean) water =Saturation concentration of oxygen in clean water,mg/I.

The Theta (θ) factor is used to relate the overall mass transfercoefficient at a specific temperature (typically standard conditions,20° C.) to that at a different temperature. Temperature strongly affectsaeration in a variety of ways. The greatest effect is on saturationdissolved oxygen concentration. The effect of saturation levels is notincluded in the theta factor, but handled in the conversion equationfrom SOR to AOR. Temperature correction of the mass transfer coefficientis achieved by applying the following equation:

    K.sub.LAT =K.sub.LA20 θ.sub.G.sup.(T-20)             (11)

where:

K_(LAT) =Mass transfer coefficient at temperature, T.

K_(LA20) =K_(LAT) corrected to Standard Conditions (BarometricPressure=1 atm, water temperature 20° C.).

θ_(G) =Geometric temperature correction coefficient, Theta.

T=Process water temperature, °C.

The correction for the effect of temperature is empirical and attemptsto lump all possible factors influencing the transfer coefficient, suchas viscosity, surface tension, diffusivity of oxygen, etc.

Proper aeration and mixing with the appropriate reactor design are thetwo most important physical design factors impacting the presentprocess. The dissolved oxygen saturation concentration in the bulkliquid decreases with increasing temperature, thus lowering the drivingforce for oxygen transfer into the bulk liquid in a thermophilicreactor. However, the oxygen transfer increases as the liquidtemperature increases and the oxygen uptake rate increases. Therefore,the oxygen uptake rate is proportional to both the overall oxygen masstransfer coefficient (K_(LA)) and the actual deficit, such that thesetwo effects cancel each other Out and high oxygen transfer efficienciesare achieved at the high thermophilic reaction temperatures. The oxygenutilization efficiencies are significantly enhanced in the hightemperature thermophilic systems encouraging high field oxygen transferefficiencies. Strong relationships exist between aeration, mixing,temperature, COD and/or VS concentration/loading rate, COD and/or VSdestruction rate, hydraulic retention time, viscosity, and amount andtype of foaming. The foam layer improves oxygen utilization and thusoxygen tansfer, enhances biological activity, and provides insulation,but it retards air flow. The foam layer is important, but it must becontrolled by densification (breaking large foam bubbles into smallbubbles) to form a compact layer above the liquid surface of thereactor. A highly efficient aeration oxygen transfer system is requiredto keep up with the extremely high oxygen utilization demand, tominimize the latent heat loss from the reactor that occurs in the airexhausted from the reactor, and to minimize energy requirements. Boththe air or oxygen flow rate and oxygen transfer efficiency depend on thereactor design geometry, turbulence and mixing conditions and organiccarbon source characteristics (soluble, particulate, viscosity, etc.).

The aerobic thermophilic treatment process can be used on hot wastes, oron wastes that provide enough fuel value for autoheating. In order toaccomplish autoheating, adequate carbon source measured as COD or VSmust be supplied to the process. The organic carbon loading can besupplied in either soluble COD form or particulate VS or COD form. Oneof the major advantages of the thermophilic process compared to themesophilic process is minimal biomass production or sludge yield whichequates to maximum heat generation. Biological heat production as highas 6,300 BTU/lb oxygen utilized has been observed. In terms ofbiological volatile solids with an oxygen equivalent of 1.42 lbs °/lb VStreated, this equates to about 9,000 BTU/lb VS destroyed. Therefore, ifthe VS or COD loading rates are high enough and proper precautions aredesigned into the treatment system to manage heat loss, the thermophilictreatment processes can be equally effective for treatment/stabilizationof biological waste sludges or high strength industrial waste (liquid orsolids) residuals. The general requirements to maintain appropriatethermophilic temperatures includes sufficient biodegradable organics (VSor COD) to provide heat of oxidation up to 25 to 30 Kcal/liter, aninsulated reactor, and adequate mixing and oxygen transfer efficiency tominimize excessive heat loss.

Exact predictions of reactor temperature must be based on material andenergy balances with the specific reactor system. A heat release of 1.0Kcal will raise the temperature of 1.0 liter of water 1.0° C. Heatproduction from organic material biodegradation and the associatedmicrobiological growth is closely related to the biomass yieldcoefficient of a given process. Biomass yield minimization results inmaximum heat generation while biomass yield maximization results inminimum heat generation. In order to achieve the critically importantobjective of autothermal operation, heat production must be maximizedand biomass generation minimized. The heat balance in autothermalprocesses is critical to both effective and economical system operation.Therefore, the key to autothermal process operation is the employment ofclosed insulated reactors for controlled heat loss where sufficient heatgeneration is achieved by maintaining appropriate organic loading ratesand microbiological or biokinetic reaction rates. Therefore, a keyprocess objective of the aerobic thermophilic process of the presentinvention is to minimize biomass yield which maximizes both heatproduction and CO₂ production. Foam control is also essential becausethe foam provides an insulating blanket on top of the reactor, as wellas improving oxygen utilization and enhancing biological activity.Efficient aeration oxygen transfer equipment is essential if the latentheat loss in the water vapor is to be maintained at an acceptable level.Evaporation losses can account for significant reductions in liquidvolume, as well as increases in heat loss in air operated systems.

A key to successful apparatus design and process operation for thepresent invention is matching the number of microorganisms in the systemto the organic substrate loading rate (COD or VS) of the system, orcontrolling the F/M ratio. Accurate prediction and modeling of treatmentperformance has been accomplished when substrate utilization isexpressed as a function of the mass substrate loading ratio (F/M) bymonomolecular kinetics for the suspended growth thermophilic treatmentsystem. Extensive evaluation of recent testing for aerobic thermophilicreactors of the present invention has shown that these systems complywith the same types of kinetic relationships previously developed by theinventor for description of mesophilic aerobic and anaerobic suspendedgrowth systems.

Extensive studies with thermophilic biological reactors by the inventorhave shown that the relationships of substrate removal versus substrateapplied were applicable to thermophilic systems. This analysis hasallowed the development of mathematical models based on the experimentaldetermination of biological kinetic constants describing substrateremoval to be applied to design and operation of the aerobicthermophilic reactors of the present invention. The mathematical modelsand application methodology, along with data from bench scale, pilotscale and full scale operating systems have been evaluated by theinventor. These models are used for the design and operation of thepresent aerobic thermophilic processes. The kinetics of substrateremoval in thermophilic treatment systems have been found to bedependent and predictable as a function of the mass substrate loading orapplication rate.

When considering the volume of the aerobic thermophilic reactor, a massbalance of substrate into and out of the reactor volume can be made asfollows: ##EQU4##

In the case of the aerobic thermophilic reactor, the reactor volume isexpressed in million gallons or cubic meters with the resultant massbalance equation: ##EQU5## where: F=Flow rate, MGD (m³ /day).

S_(i) =Influent substrate concentration, mg/l.

S_(e) =Effluent substrate concentration, mg/l.

V=Reactor volume in million gallons (cubic meters).

(dS/dt)_(G) =Substrate utilization rate, lbs substrate/day/lb reactorvolatile suspended solids (Kgs substrate/day/Kg reactor volatilesuspended solids).

Mathematical description of this substrate utilization rate as afunction of the substrate loading rate or F/M ratio based onmonomolecular kinetics follows: ##EQU6## where: X=Reactor mixed liquorvolatile suspended solids concentration, mg/l.

FS_(i) /XV=Mass substrate loading rate, lbs substrate/day/lb reactorvolatile suspended solids (Kgs substrate/day/Kg reactor volatilesuspended solids).

U_(max) =Maximum specific substrate utilization rate, lbssubstrate/day/lb reactor volatile suspended solids (Kgs substrate/day/Kgreactor volatile suspended solids).

K_(B) =Proportionality constant or substrate loading at which the rateof substrate utilization is one-half the maximum rate, lbssubstrate/day/lb reactor volatile suspended solids (Kgs substrate/day/Kgreactor volatile suspended solids).

Substitution of Equation 14 into Equation 13 and solving for the reactorvolume, V or the effluent quality, S_(e), provides the design equationor the effluent quality predictive equation to be used for operation,respectively. The kinetic constants, U_(max) and K_(B), are determinedexperimentally.

The formula for the specific substrate utilization rate is as follows:##EQU7## where U=Specific substrate utilization rate, lbssubstrate/day/lb reactor volatile suspended solids (Kgs substrate/day/Kgreactor volatile suspended solids).

The specific substrate utilization rate (U) is plotted as a function ofthe specific substrate loading rate or mass substrate loading rate. Thenthe reciprocal of U is plotted as a function of the reciprocal of themass loading rates. U_(max) is the reciprocal of the Y-axis intercept,and the slope of the line is equal to K_(S) /U_(max).

It is important during start-up and operation of the aerobicthermophilic reactor 10 to acclimate and stabilize the reactor vessel 12with thermophilic microorganisms. The thermophilic biological solidsinventory is increased by gradually increasing the flow of wastematerial, and thus the organic loading rate (COD and/or VS), to thereactor vessel 12. It is important to increase the organic loadings anddecrease the hydraulic retention times as the temperature of the bulkliquid in the reactor vessel 12 increases in proportion to the quantityof thermophilic biomass in order to control the food-to-microorganism(F/M) ratio and biological solids retention time in the reactor. Thisaspect of both reactor start-up and stabilized operations can bemonitored by the previously described critical parameters. Adjustmentsare required when any of the parameters exceed pre-set acceptableoperating ranges.

In summary, the present invention provides an aerobic thermophilictreatment process coupled with a novel reactor design to offersignificant advantages, compared with the prior art, in terms oftreatment performance, process optimization, biogas and offgas quality,and capabilities to treat complex, inhibitory, and difficult to treatindustrial wastes.

It will be clear that the present invention is well adapted to attainthe ends and advantages mentioned as well as those inherent therein.While presently preferred embodiments have been described for purposesof disclosure, numerous changes may be made which will readily suggestthemselves to those skilled in the art and which are encompassed in thespirit of the invention disclosed and as defined in the appended claims.

What is claimed is:
 1. An aerobic thermophilic process for treatingwaste comprising:injecting waste material into a reactor vessel havingthermophilic microorganism to form a volume of bulk liquid in thereactor vessel; injecting an oxygen-containing gas into the reactorvessel in such manner as to transfer oxygen into the reactor bulk liquidfor utilization by the thermophilic microorganisms in aerobic treatmentof the waste material; monitoring the oxidation-reduction potential andtemperature of the reactor bulk liquid; monitoring the concentration ofvolatile fatty acids and sulfides in the reactor bulk liquid; andadjusting at least a selected one of the rate of injection of theoxygen-containing gas, the oxygen-transfer efficiency of theoxygen-containing gas and the volume of bulk liquid in the reactor inresponse to the concentration of volatile fatty acids, concentration ofsulfides, oxidation-reduction potential and temperature of the reactorbulk liquid to maintain the temperature of the reactor bulk liquidwithin a predetermined range.
 2. An aerobic thermophilic process fortreating waste comprising:injecting waste material into a reactor vesselhaving thermophilic microorganisms to form a volume of bulk liquid inthe reactor vessel; injecting an oxygen-containing gas into the reactorvessel in such manner as to transfer oxygen into the reactor bulk liquidfor utilization by the thermophilic microorganisms in aerobic treatmentof the waste material; monitoring the oxidation-reduction potential andtemperature of the reactor bulk liquid; monitoring the concentration ofvolatile fatty acids and sulfides in the reactor bulk liquid; removingoffgas from the reactor vessel; monitoring the concentration of oxygen,hydrogen sulfide and carbon dioxide in the offgas; and adjusting atleast a selected one of the rate of injection of the oxygen-containinggas, the oxygen-transfer efficiency of the oxygen-containing gas and thevolume of bulk liquid in the reactor in response to the concentrationsof oxygen, hydrogen sulfide and carbon dioxide in the offgas, and inresponse to the concentration of volatile fatty acids, concentration ofsulfides, oxidation-reduction potential and temperature of the reactorbulk liquid to maintain the temperature of the reactor bulk liquidwithin a predetermined range.
 3. An aerobic thermophilic process fortreating waste comprising:injecting waste material into a reactor vesselhaving thermophilic microorganisms to form a volume of bulk liquid inthe reactor vessel; injecting an oxygen-containing gas into the reactorvessel in such manner as to transfer oxygen into the reactor bulk liquidfor utilization by the thermophilic microorganisms in aerobic treatmentof the waste material; monitoring the oxidation-reduction potential andtemperature of the reactor bulk liquid; monitoring the concentration ofvolatile fatty acids and sulfides in the reactor bulk liquid; removingoffgas from the reactor vessel; monitoring the concentration of oxygen,hydrogen sulfide and carbon dioxide in the offgas; monitoring the levelsof alkalinity, COD, TS, VS, NH₃ --N and PO₄ --P for the process; andadjusting at least a selected one of the rate of injection of theoxygen-containing gas, the oxygen-transfer efficiency of theoxygen-containing gas and the volume of bulk liquid in the reactor inresponse to the concentrations of oxygen, hydrogen sulfide and carbondioxide in the offgas, and in response to the alkalinity, COD, TS, VS,NH₃ --N, PO₄ --P, concentration of volatile fatty acids, concentrationof sulfides, oxidation-reduction potential and temperature of thereactor bulk liquid to maintain the temperature of the reactor bulkliquid within a predetermined range.
 4. An aerobic thermophilic processfor treating waste comprising:injecting waste material into a reactorvessel having thermophilic microorganisms to form a volume of bulkliquid in the reactor vessel; injecting an oxygen-containing gas intothe reactor vessel in such manner as to transfer oxygen into the reactorbulk liquid for utilization by the thermophilic microorganisms inaerobic treatment of the waste material; monitoring theoxidation-reduction potential and temperature of the reactor bulkliquid; monitoring the concentration of volatile fatty acids andsulfides in the reactor bulk liquid; and adjusting at least a selectedone of the rate of injection of the oxygen-containing gas, theoxygen-transfer efficiency of the oxygen-containing gas and the volumeof bulk liquid in the reactor in response to the concentration ofvolatile fatty acids, concentration of sulfides, oxidation-reductionpotential and temperature of the reactor bulk liquid to maintain thetemperature of the reactor bulk liquid within a predetermined range. 5.An aerobic thermophilic process for treating waste comprising:injectingwaste material into a reactor vessel having thermophilic microorganismsto form a volume of bulk liquid in the reactor vessel; injecting anoxygen-containing gas into the reactor vessel in such manner as totransfer oxygen into the reactor bulk liquid for utilization by thethermophilic microorganisms in aerobic treatment of the waste material;monitoring the oxidation-reduction potential and temperature of thereactor bulk liquid; monitoring the concentration of volatile fattyacids and sulfides in the reactor bulk liquid; removing offgas from thereactor vessel; monitoring the concentration of oxygen, hydrogen sulfideand carbon dioxide in the offgas; and adjusting at least a selected oneof the rate of injection of the oxygen-containing gas, theoxygen-transfer efficiency of the oxygen-containing gas and the volumeof bulk liquid in the reactor in response to the concentrations ofoxygen, hydrogen sulfide and carbon dioxide in the offgas, and inresponse to the concentration of volatile fatty acids, concentration ofsulfides, oxidation-reduction potential and temperature of the reactorbulk liquid to maintain the temperature of the reactor bulk liquidwithin a predetermined range.
 6. An aerobic thermophilic process fortreating waste comprising:injecting waste material into a reactor vesselhaving thermophilic microorganisms to form a volume of bulk liquid inthe reactor vessel; injecting an oxygen-containing gas into the reactorvessel in such manner as to transfer oxygen into the reactor bulk liquidfor utilization by the thermophilic microorganisms in aerobic treatmentof the waste material; monitoring the oxidation-reduction potential andtemperature of the reactor bulk liquid; monitoring the concentration ofvolatile fatty acids and sulfides in the reactor bulk liquid; removingoffgas from the reactor vessel; monitoring the concentration of oxygen,hydrogen sulfide and carbon dioxide in the offgas; monitoring the levelsof alkalinity, COD, TS, VS, NH₃ --N and PO₄ --P for the process; andadjusting at least a selected one of the rate of injection of theoxygen-containing gas, the oxygen-transfer efficiency of theoxygen-containing gas and the volume of bulk liquid in the reactor inresponse to the concentrations of oxygen, hydrogen sulfide and carbondioxide in the offgas, and in response to the alkalinity, COD, TS, VS,NH₃ --N, PO₄ --P, concentration of volatile fatty acids, concentrationof sulfides, oxidation-reduction potential and temperature of thereactor bulk liquid to maintain the temperature of the reactor bulkliquid within a predetermined range.